Main steam line desuperheater systems,apparatus and method



Feb. 24, 1970 c. DQWILSON 3,

MAIN STEAM LINE DESUPERHEATER SYSTEMS, APPARATUS AND METHOD 7 Sheets-Sheet l Filed Nov. 50, 1967 ff! 0 0 J8 77-1 A I; f i 4 1 A av! F 52 PF? ,7?) m PF4 Pf? 4/14 M/MMOP ,Q VW fi/ -1 mz ?MK M Feb. 24., 1970 c. D. WILSON 3,496,724

MAIN STEAM LINE DESUPERHEATER SYSTEMS, APPARATUS AND METHOD Filed Nov. 30, 1967 7 Sheets-Shet 2 'BHD BEMBGHBBIEHi "JAJK 5/ /9 QIXABMAA 'Feb. '24, 1970 C. D. WILSON MAIN STEAM LINE DESUPERHEATER SYSTEMS Filed Nov. 30, 1967 APPARATUS AND METHOD 7 Sheets-Sheet 5 .16; 1/; 4 if; y

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MAIN STEAM LINE DESUPERHEATER SYSTEMS, APPARATUS AND METHOD Feb. 24, 1910 c. D. WILSON 3,496,724

MAIN STEAM LINE DESUPERHEATER SYSTEMS, APPARATUS AND METHOD Filed Nov 30. 19a"? 7 Sheets-Sheet 5 FI'T h 3Z6 ii 5 I if 11 H 1w 1% g 4 5 3/36? Feb. 24, 1970 c. D. WILSON 3,

MAIN STEAM LINE DESUPERHEATER SYSTEMS, APPARATUS AND METHQD Filed Nov. 50, 19s? 7 sheets sheet 6 64; f -5 a fl n f 615 mp 64 L Ki/[E I UULUUM? Y fa f 944 VA T )9 w! j A j ,g wz

Feb. 24., 1970 c. .3, WILSON 3,496,724

MAIN STEAM LINE DESUPERHEATER SYSTEMS, APPARATUS AND METHOD AM/w United States Patent 3,496,724 MAIN STEAM LINE DESUPERHEATER SYSTEMS, APPARATUS AND METHOD Charles D. Wilson, West Allis, Wis., assignor to Allis- Chalmers Manufacturing Company, Milwaukee, Wis. Filed Nov. 30, 1967, Ser. No. 687,060 Int. Cl. F01k 13/00; F22b 33/00; F22g 5/12 U.S. Cl. 60-105 25 Claims ABSTRACT OF THE DISCLOSURE A system, apparatus and method for controlling the temperature of steam supplied to a turbine .or the like to maintain a satisfactory temperature gradient in the metal of the turbine during the starting and loading cycle or during the unloading cycle. A desuperheater device is installed in the steam line between the boiler and the turbine. Cooling water is supplied to the desuperheater device for injection into the main steam flow in a restricted passage region and at the proper water flow rate to maintain proper steam temperature for the required temperature gradient of the turbine metal. The desuperheater device includes an adjustable valvelike plug member which is movable in response to the sensed steam pressure differential thereacross to maintain steam pressure and velocity across the restricted passage at proper values to obtain optimum atomization of the cooling water under changing steam flow and pressure conditions.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to a system and apparatus for and a method of controlling the temperature .of steam entering a steam turbine to maintain a satsifactory temperature gradient in the metal of the turbine whereby to prevent distortion of the meal clue to thermal stress. The apparatus of the invention also has utility in other steam systems where it is desired to control the temperature of steam by a desuperheating action.

To allow turbines to start and pick up load quickly, the temperature .of steam entering the turbine must be controlled and temperature changes must be limited to between 100 F. and 150 F. per hour. I

If temperatures change at a faster rate than this, temperature gradients will occur across cylinder walls and across heavy sections of the rotating shaft that will be large enough to cause distortion and excessively high thermal stresses. If this practice is continued, eventual cracking and even failure of the members can be expected.

In order to avoid damage to the turbine, it has been the practice to start and load the turbine slowly so as to avoid increasing the temperature at too fast a rate. In many installations, these limitations require as much as eight hours or more before a cold machine can be put .on the line and brought up to full load. Even when starting warm machines after overnight shutdowns, extreme caution must be used when starting, and the reaching of full load is .often delayed for several hours. Since the load factor on many generating systems requires overnight shutdown of many units, this difliculty in restarting has resulted in poor efficiency in operation and has required maintaining more than the desired amount of spinning reserve on the line to protect the system. Shortcuts taken when fast starting during emergencies, have often resulted in unnecessary damage with the resulting need for repairs being inflicted on generating equipment.

In the prior art, it has also been necessary to remove load from the turbine gradually over an extended period 3,496,724 Patented Feb. 24, 1970 of time in order to avoid thermal shock to the turbine.

Boilers are usually designed for full load (maximum flow) condition and as soon as load is increased and the steam flow through the boiler becomes larger, steam temperatures quickly increase to approach rated temperatures. This results in steam temperature to the turbine increasing at a faster rate than the turbine can safely accommodate. By various means such as selective firing of burners, by using tilting burners, by baffling hot gases and diverting some gases to the stack, and by attemperating (desuperheating) at various points inside the boiler, attempts have been made in the boiler design to control the steam temperature to satisfy turbine startup and load change requirements.

These attempts of the prior art to control steam temperature as just described have never been completely successful. They have complicated the operation of the plant and have still required load restrictions when starting in order to properly control temperature. Some positive means for controlling the steam temperature to the turbine during the starting and loading cycle, as well as during the unloading cycle, is necessary in order to permit the turbine to be started and loaded or to be unloaded quickly, safely and efiiciently. A control that would do this would be especially desirable for the lar e steam turbine generator units used on utility systems where cyclic variations in system load require frequent starting and stopping of these large machines.

There would be no limit on how quickly a turbine could be started and brought up to full load if the steam supplied to the turbine was the same temperature as the turbine or, at most, not more than F. hotter than the turbine.

While many types of desuperheating devices are known for controlling steam temperature, most of the available types of desuperheater equipment are designed for application on constant steam how at constant temperature conditions. Since such desuperheater equipment does not operate elfectively when conditions vary too much from the conditions as specified, they are not suitable for controlled starting applications on steam turbines where conditions vary over a wide range. Furthermore, many of the available desuperheaters constitute obstructions in the steam line even when the desuperheater is not in use.

By controlling the steam temperature to the turbine, and particularly by controlling the temperature by means in the main line between the boiler and the turbine rather by means of controls within the boiler, a number of advantages, and economic and timesaving benefits are obtained.

For example, boiler operation becomes simplified because the boiler can then be operated to satisfy the optimum requirements of the boiler without having to make special control adjustments in the boiler to satisfy turbine limitations on rates of temperature change.

The operator will also be able to start and load the turbine in much less time and do so without exceeding the allowable limits of temperature change that cause hidden thermal shock damage and eventual expensive maintenance.

The main steam line desuperheater system of the invention can also be used to cool the turbine at a controlled rate prior to shutdown. The turbine can be cooled while the unit is still carrying high loads, so that when the unit is taken out of service, the turbine metal temperatures will be at the correct value for the next scheduled startup. This makes it possible to shut the turbine down quickly when it is no longer needed and avoids the formerly required extended operating time at reduced load when taking the unit out of service.

With the much faster starting, loading and unloading that becomes possible, the availability of the turbine is increased, and the turbine generator unit becomes more adaptable for peaking service and part-time cyclic operation.

At the same time, by avoiding condition that could cause hidden thermal shock damage with a resulting loss in operating efficiency, and the need for increased maintenance, the interval between outages for scheduled service inspections should be greatly increased.

On reheat machine, the desuperheater system can be applied to both the primary and reheat inlets to provide independent temperature control for each inlet which can be preset by the operator to suit the specific requirements of the turbine.

The desuperheater control can be operated with fully automatic operation. However, it is recommended that the initial control settings be established and manually set by the operator. After placing the desuperheater in service, a clock-operated program cycle can then be used to increase or decrease the control setting temperature at a prescribed rate, or the control settings can be manually readjusted as required by the operator.

SUMMARY OF THE INVENTION Accordingly, it is an object of this invention to provide an apparatus and method for controlling the temperature of steam entering a steam turbine particularly during the starting, loading or unloading of the turbine, whereby to maintain a satisfactory temperature gradient in the metal of the turbine and thereby prevent distortion of the metal due to thermal stress.

It is another object of the invention to provide an apparatus and system for controlling steam temperature to turbines which permits much faster starting, loading and unloading of the turbine than was possible in the prior art.

It is another object of the invention to provide an apparatus and method for progressively changing the temperature of steam supplied to a turbine during the loading or unloading of the turbine to prevent distortion of the metal due to thermal stress.

It is another object of the invention to provide a desuperheater having an adjustable passage area to give a high fluid velocity of the steam for eflicient atomization of the cooling fluid.

It is another object of the invention to provide a desuperheating apparatus and system in which the injected desuperheating water is atomized to an optimum extent under all steam flow and pressure conditions.

It is another object of the invention to provide a desuperheating apparatus for turbines which is separate from the boiler and the turbine and is installed in the steam line between the boiler and the turbine, and which can be applied on both new and old installations to control the temperature of steam entering the turbine.

It is another object of the invention to provide a desuperheater apparatus which is adapted for use under changing steam flow and pressure conditions and which can be retracted to a position in which it does not obstruct the steam line when not in use.

Still another object of the invention is to provide a desuperheater apparatus which is so constructed as to avoid direct contact between the cooling water and the high temperature desuperheating casing and steam header.

In achievement of these objectives, there is provided in accordance with the invention, a system, apparatus and method for controlling the temperature of steam supplied to a turbine or the like to maintain a satisfactory tem perature gradient in the metal of the turbine during the starting and loading cycle or during the unloading cycle. A desuperheater device is installed in the steam line between the boiler and the turbine. Cooling water is supplied to the desuperheater device for injection into the main steam flow in a restricted passage region and at the proper Water flow rate to maintain proper steam temperature for the required temperature gradient of the turbine metal. The desuperheater device includes an adjustable valvelike plug member which is movable in response to the sensed steam pressure differential thereacross to maintain steam pressure and velocity across the restricted passage at proper value to obtain optimum atomization of the cooling water under changing steam flow and pressure conditions.

In accordance with a further feature of the invention, the temperature of the steam may be automatically changed in either an increase or decrease direction, and at any one of a plurality of predetermined rates.

Another feature includes a modified desuperheater construction in which the cooling water is mixed with bypass steam and is thereby subjected to atomization prior to being injected into the main steam flow, where further atomization occurs. This feature minimizes any thermal shock to the fluid transmitting casing which might be caused by the direct injection of the cooling water into the main steam flow.

In accordance with a still further feature, the cooling water manifold and the conduits leading thereto are substantially thermally isolated from the hot desuperheater casing to prevent thermal shock to the desuperheaer casing due to the cooling water. Also, a thermal shield is positioned in the desuperheater casing contiguous the region of cooling water injection and downstream thereof to prevent thermal shock to the steam transmitting casing caused by direct contact with the cooling water.

Further objects and advantages of the invention will become apparent after the following description, taken in conjunction with the following drawings in which:

BRIEF DESCRIPTIONVOF THE DRAWINGS FIG. 1 is a schematic diagram of the desuperheater system and apparatus of the invention;

FIG. 2 is a view in vertical section showing the desuperheater apparatus of the invention mounted in the steam header between the boiler and the turbine;

FIG. 3 is a view in vertical section showing details of the water injection inlet construction which forms part of the desuperheater apparatus;

FIG. 4 is a view in vertical section of a modified water injection inlet construction for the desuperheater apparatus;

FIG. 5 is a view in horizontal section, taken along line V-V of FIG. 2 through the desuperheater showing details of the cooling water manifold and of the inlet piping connections to the cooling water manifold;

FIG. 6 is a view in longitudinal section of a control device used in connection with control loop A to maintain a constant pressure drop across the desuperheater restricted flow passage;

FIG. 7 is a schematic wiring diagram for control loop A;

FIG. 8 is a view in section of an operating mechanism which may be used for raising and lowering the desuperheater Valve plug;

FIG. 9 is a view in vertical section of a cooling water admission valve and of the pneumatic operator therefor forming part of the desuperheater system;

FIG. 10 is a schematic view of the steam temperature controller with manual and automatic preset which may be used with the desuperheater system of the apparatus;

FIG. 11 is a wiring diagram for control loops B and C used in connection with controlling the steam temperature of the desuperheater system;

FIG. 12 is a wiring diagram for control loops D, E, F and G;

FIG. 13 is a view in vertical section of the water dump valve and of the pneumatic operator therefor, forming part of the desuperheater system; and

FIG. 14 is a control operator which may be used for protection against excessive steam cooling due to sudden load drop on the turbine.

Referring now to FIGS. 1 and 2, there is shown a desuperheating casing generally indicated at 14 installed in the steam line or header between boiler and turbine 18. The desuperheater casing is an elbow shaped member including a section which is weldedly connected to the steam line 12 from boiler 10 and a section 22 which extends along an axis at right angles to the elbow section 20 and is weldedly connected to steam line 16 leading to turbine 18. The upper end of the desuperheater casing 14 is provided with a cover member 26. A downwardly open hollow hublike guide member 28 extends from the under surface of cover 26. Cover 26 is provided with an upper passage 30 which communicates with the downwardly open hollow interior 32 of hub 28. A guide bushing 34 is positioned in the upper passage 30 and a guide bushing 36 is positioned in the lower portion of the hub 28.

The vertically adjustable desuperheater valve plug is generally indicated at 38 and includes a disk-shaped lower portion 40 and an integral upstanding portion 42 having a vertical passage therethrough to receive the lower end of operating stem 44. The lower end of operating stem 44 is provided with a shoulder 46 Which is received in the counterbore 48 in the lower face of disk portion 40 of the valve plug. Nut member 50 engages a threaded portion of operating stem 44 and engages the upper edge of portion 42 of the desuperheater valve plug 38 to maintain operating stem 44 rigidly assembled relative to desuperheater valve plug 38. The upper end of the operating stem is guided by bushing 34 and projects above the upper end of top cover 26, being guided by suitable support and guide means mounted on cover 26. An operating means generally indicated at 52 driven by an electric motor 54 (see FIG. 8) is provided to move the operating stem 44 up or down, thereby varying the position of the desuperheater valve plug 38. Valve plug 38 is guided for vertical movement by bushing 36. Motor 54 is controlled by control loop A (FIG. 1) in response to steam pressure signals from transducers PT1 and PT-Z (FIG. 1), respectively upstream and downstream of the moveable desuperheater valve plug 38. Details of the operating means 52 and of control loop A will be described hereinafter.

The desuperheater valve plug 38 operates on the principle of providing a restricted passage and thereby creating a high steam velocity to promote optimum cooling water atomization and evaporation in the region of cooling water injection. When the desuperheater is in operation, the passage area X at the point of cooling water injection, to be explained hereinafter in more detail, is automatically adjusted by the motor operator 52 by axially varying the position of the desuperheater valve plug 38 to obtain a predetermined constant pressure drop across the valve plug and constant local steam velocity in the restricted steam passage defined by disk portion 40 of valve plug 38, and by the surfaces contiguous thereto for all steam flows through the desuperheater casing 14. When the desuperheater is not in operation, the desuperheater valve plug 38 can be withdrawn by the motor operator 52 to its uppermost position to obtain an unobstructed steam passage through the desuperheater casing with minimum pressure drop.

The guide bushing 36 is provided with a back seat surface 56 which cooperates with a similar surface at 58 on valve plug 38 to prevent steam leakage upwardly through the valve support guide structure when the valve plug is in wide open position and the desuperheater is not in use.

A low pressure steam leakolf, indicated at 60, is provided in communication with space 32. The guide bushing 36 and the steam passage diameters are proportioned so that the resultant steam forces acting on the desuperheater valve plug 38 and on the operating stem 44 will always be in an upward direction for all normal operating positions of the desuperheater valve plug. This is done to increase valve stability and to reduce the possibility of chattering.

Steam flow enters the enlarged chamber 29 (FIG. 2)

in the desuperheater casing Where the line velocity is reduced before the direction of flow is changed. A fiow divider 31 is provided in the chamber to avoid swirling. The steam flow then changes direction and passes down into the area where the cooling water is injected and the steam flow velocity is increased through the restricted passage to assist in atomizing and evaporating the cooling water.

As best seen in FIGS. 2 and 3, the desupcrheating casing 14 is provided with an annular recess or shoulder 64 to receive an annular cooling water supply manifold generally indicated at 62. Water is supplied under pressure to the manifold 62 from the boiler feed pump discharge, in series with a water admission valve 300 which will be described in more detail later and which controls the rate at which water is admitted to the manifold 62.

The manifold 62 includes a radially outer wall 66 and upper and lower radially inwardly extending walls 67 and 68. A suitable closure plate 69 is rigidly attached as by welding to the respective inner peripheral surfaces of the respective upper and lower walls 67 and 68 to thereby close the annular manifold on the radially inner periphery thereof. A large number of circumferentially or peripherally spaced outlet nozzles 70 are machined in the upper Wall 67 of the manifold in communication with the interior of hollow manifold chamber 62, these nozzles being inclined radially inwardly and upwardly.

A circumferentially extending baffle plate 72 is mounted on the upper wall 67 of manifold 62, the radially inner portion of the baffle plate being provided with a groove 74 in overlying relation to the nozzles 70. Cap screws 76 have the upper ends thereof received in countersunk recesses of the bafile plate 72 and extend downwardly through bafile plate 72 and manifold member 62, and have the lower ends thereof received in threaded passages in the desuperheater casing 14 to thereby secure the baffle plate and the manifold securely in position on the desuperheater casing. The radially inner surface of the desuperheater casing 14 is provided with a radially inwardly projecting rib 71 (FIG. 3) which engages the radially outer wall surface 66 of the water manifold and thereby spaces the major portion of wall 66 of the cooling water manifold out of heat transfer relation, with respect to the high temperature desuperheater casing 14, thereby avoiding thermal shock to the casing 14. Similarly, to minimize contact between the bottom wall 68 of the cooling water manifold and the hot desuperheater casing 14 to minimize thermal shock to the desuperheater casing, the bottom wall 68 is arched as indicated at 73 (FIG. 3) with only minimal contact being made with the surface of the desuperheater casing 14 by the riblike members 75. The groove 74 of battle plate 72, as well as the groove-bounding surface of upper wall 67 of manifold 62, and the upper and radially inner surfaces of wall 69 of the cold water manifold are lined with an erosion resistant material such as stainless steel, as indicated at 77 (FIG. 3).

As seen in FIGS. 3-5, inclusive, two diametrically opposite water supply pipes 78 or 78' are received by a slide fit in passages 79 or 79' of the annular cooling water sup-ply manifold 62 or 62' the water supply pipes 78 or 78 being connected internally to the cold water manifold by a sliding socket connection which is sealed by special alloy steel piston ring seals 80' or 80. The two inlet pipes 78 or 78' are connected to a T-connection 81 into which the cooling water is admitted from a suitable supply source, such as the discharge from the boiler feed pump. The annular cooling water supply manifold 62 can be removed for inspection and servicing after lifting the desuperheater casing cover 26, by removing cap screws 76 which secure manifold 62 to desuperheater casing 14.

In order to maintain the cold water inlet pipes 78 out of direct contact with the hot desuperheater casing 14 and, thus, avoid thermal stress on the casing 14, each pipe 78 passes through and is welded to a flange member 82 (FIG. having a neck portion 83 which engages the outer diameter of each respective pipe 78 and maintains the pipe 78 out of contact with the larger diameter passage 84 in flange 82 and desuperheater casing 14, thereby substantially avoiding any thermal contact between pipe 78 and the hot desuperheater casing 14. Flange 82 is secured in position on the desuperheater casing by studs 85 energized by nuts 87.

In the water injection arrangement shown in FIG. 3, the annular water manifold 62 discharges cooling water through the large number of closely spaced orifice holes or nozzles 70 into the main steam flow in the region of the adjustable high velocity restricted passage X as defined by the position of movable desup-erheating valve plug 38 relative to the adjacent surfaces of baffle 72 and the radially inner wall 69 of water manifold 62. Orifice holes or nozzles 70 are uniformly spaced around the circumference of the water manifold 62. The flow of cooling water is automatically controlled by regulating valve 300, to be described more fully hereinafter, which is responsive to downstream steam temperature as detected by thermocouple TT5 (FIG. 1). When the steam flow is light and the desuperheating water flow is small, the cooling water flows over the stainless steel inlay passage surface 77 (FIG. 3) until it is picked up, atomized and evaporated by the main steam line flow, which is accelerating to pass through the restricted passage. When the steam flow is heavy and the cooling water flow is larger, the cooling water will form jets as it passes through the orifice holes 70 which act as discharge nozzles. The jets will be deflected by the stainless steel inlaid deflector plate 77 to form fanlike sprays which will distribute the cooling water into the main steam flow just before it enters the high velocity passage.

As best seen in FIGS. 1 and 2, in order to prevent thermal shock to the desuperheater casing and to the contiguous areas of the header portion 16 to which the desuperheater casing is weldedly attached, due to the impingement of cooling water on the hot surfaces of these members, a cylindrical thermal shield 88 of thin metal is suitably mounted inside these members in radially in wardly spaced relation thereto. The thermal shield may extend for a distance such as four feet, for example, and in the region through which it extends will prevent any contact between the cooling water and the desuperheater casing 14 or contiguous header 16, thereby avoiding thermal stress on the hot desuperheater casing and adjacent portions of the connected header.

The water manifold 62' of FIG. 4 is generally similar to the manifold 62 of FIG. 2, previously described, in that it includes a radially outer wall 66, top and bottom walls 67, '68 and a radially inner wall 69 which together define a manifold having a hollow annular water chamber.

Cooling water is admitted to the interior of the manifold by water pipes 78, as in the embodiment of FIG. 3. A plurality of outlet nozzles 70' communicate with the interior of the hollow manifold and communicate with annular groove or mixing chamber 74' defined by baffle plate 72 mounted on the upper surface of top wall 67' of the water manifold.

An erosion preventing inlay 77 is provided on the groove-defining surfaces of the baffle plate and the contiguous surfaces of the water manifold, as in the embodiment of FIG. 3.

The modified embodiment of FIG. 4 differs from the embodiment of FIG. 3 in that a large number of circumferentially spaced inlet openings or passages 100 are provided in the baflle or cover plate member 72', these inlet openings extending inwardly from the radially outer face of the baflle 72' in such manner as to define bypass steam flow passages 100 which communicate with an annular steam manifold 102 formed in the cooperating facing surfaces of the top wall 67' of water manifold 62' and of the baffie or cover plate 72'. Steam manifold 102 is connected by a large number of circumferentially spaced slots or nozzles 104 with the shielded annular mixing chamber 74 which, in turn, communicates with water discharge nozzles 70 of water manifold 62. Since the entrance to the bypass steam passages is on the upstream side above the normal operating location of valve plug 38, the steam pressure P A at the entrance to bypass flow passages 100 is higher than the steam pressure P at the discharge end of the shielded mixing chamber 74 adjacent the restricted passage X defined by desuperheater valve 38. The pressure P in the restricted passage is less than P due to the high steam velocity in the restricted passage. This differential in pressure causes the flow of bypass steam through passages 100, the slots 104, and into the shielded mixing chamber 74 where the bypass steam mixes with the cooling water and atomizes it before the mixture is injected into the main line steam flow. Thus, the initial mixing of the water and steam occurs in a shielded region, namely the shielded mixing chamber 74', which is isolated from the main steam flow. The mixture is then injected into the main steam flow at the restricted passage X adjacent the discharge end of the shielded mixing chamber 74, at a region where high steam velocity exists. The Water-steam mixture is there subjected to a second steam atomizing action to get optimum evaporation of the water.

By first mixing the cooling water with bypass steam in a separate shielded mixing chamber, as just described, the temperature changes in the desuperheater casing will be less drastic and the possibility of thermal shock in the heavy Walled casings containing the main header steam flow will be minimized.

CONTROL LOOP A FOR CONTROLLING POSITION OF DESUPERHEATER VALVE There is shown in FIG. 6 a control arrangement which may be used in control loop A of FIG. 1 to control the position of the desuperheater valve plug 38 to maintain a predetermined desired pressure drop between the point PT-l which is upstream of the valve plug 38 and the point PT2 which is downstream of the valve plug 38, this predetermined pressure drop being of a value which produces a steam velocity in the region of valve 38 which insures optimum atomization of the cooling Water injected in the region adjacent the desuperheater valve. This predetermined pressure drop is maintained for all boiler steam pressures and for all main line steam flows.

The control device includes a casing generally indicated at which is divided into two chambers 112 and 114 by a flexible diaphragm member 116. The chambers 112 and 114 are respectively subjected to the respective steam pressures P and P from the points PT-2 and PT-1 (FIG. 1). The diaphragm 116 is connected to and moves a switch operating shaft 118 which is supported for linear movement by bearing passages in the opposite walls of casing 110. Stop members 120 are fixed to the shaft 118 to limit the movement thereof in opposite directions. The shaft 118 carries a spring seat 122 at the outer or righthand end thereof with respect ot the view shown in FIG. 6. A spring 124 is interposed between the spring seat 122 and the facing end wall 125 of casing 110.

It will be seen that the spring 124 tends to move the shaft 118 in the same direction as the downstream pressure P in chamber 112. For example, the spring may be so calibrated that it just balances the forces on the diaphragm when P P =l00 p.s.i. An abutment 126 is carried by and movable with shaft 118.

The spring scale is such that the shaft 118 will move a 100 plus 25 p.s.i. or higher, and to operate limit switch LS-2 when the pressure difference is 100 minus 25 p.s.i. or lower. The control can be adjusted to operate at higher or lower pressure differentials by changing the pressure on the balancing spring 124 and by repositioning limit switches LS-l and LS-2.

As best seen in the wiring diagram of FIG. 7, limit switches LS-l and LS-2 each have one normally open and one normally closed contact.

Contact LS-la is normally open, and closes to energize solenoid 8-1 when the pressure drop P P exceeds 125 p.s.i. Closure of solenoid S-l closes contacts S 1a and S-lb in the starting circuit of the reversing motor 54 to cause the operating mechanism 52 to start raising the valve vplug 38 to increase the steam passage area and reduce the pressure drop across the plug.

Limit switch contact LS-2a is normally open and closes to energize solenoid S2 when the pressure drop P P across the valve is less than 75 p.s.i. Energization of solenoid S2 closes contacts S2a and S2b in the starting circuit of reversing motor 54 to cause motor 54 t actuate operating mechanism 52 to start lowering valve plug 38 to decrease the steam passage area in the vicinity of the plug, to thereby increase the pressure drop across the plug.

As seen in the wiring diagram of FIG. 7, limit switch contacts LS-lb and LS-2b are both normally closed and when the pressure drop is between 75 p.s.i. and 125 p.s.i., they operate signal light L-3 to indicate that the desuperheater is operating within the normal range of pressure drop. If the pressure drop is either above 125 p.s.i. or below 75 p.s.i., either LS-1b or LS2b will open to turn off signal light L-3.

Limit switch LS3 has one normally open and one normally closed contact. It is mounted on the desuperheater and operates when the valve plug 38 is open wide against the back seat.

Control switch CS-l is an On and Off switch. When it is in Off position and valve plug 38 is against the back seat, normally open limit switch contact LS3b is closed to operate the signal light L1. If the valve plug 38 is not against the back seat, limit switch contact LS-3a, which is normally closed, will energize solenoid 8-1 to start to move the valve plug 38 against the back seat. When the valve plug 38 reaches the back seat, LS-3a will then open to deenergize solenoid S-1 and stop the movement of the valve plug 38, and LS-3b will close to energize light L1 to indicate that the valve plug is against the back seat.

When control switch CS-l is moved from Off to On, it operates signal light L-2 and completes the circuits to limit switches LS-l and LS-2 so that they function. The On position of control switch CS-l disconnects limit switch LS3 from the circuit and turns off signal light L-1.

MECHANISM FOR MOVING DESUPERHEATER VALVE As best seen in FIG. 8, the operating means 52 for the valve stem 44 comprises a planetary reduction gear 200 driven by the motor 54 and having an output shaft 202 supported by spaced bearing brackets 204, 206. Motor 54, planetary reduction gear 200, output shaft 202, and bearing brackets 204, 206 are all carried by a support 215 which is pivotally supported at 221 on stationary support 214. Shaft 202 is threaded as indicated at 208 and a nut 210 is movable in either a forward or reverse direction along the threaded shaft 202 in accordance with the direction of rotation of shaft 202. A bell crank 212 is pivotally mounted at 218 on stationary bracket member 214. The upper end of hell crank 212 is connected by trunnions 216 to the nut 210, whereby as the nut is moved in one direction or the other along shaft 202, bell crank 212 is caused to pivot about its pivot point 218. The upper end of valve stem 44 is provided with a clevis 220 which is pivotally connected at the upper end thereof to a link 10 222, the opposite end of link 222 being pivotally connected at 224 to the outer end of the bell crank 212.

It will be seen therefore, that as motor 54 rotates shaft 202 through planetary reduction gear 200 that nut 210 will be linearly moved along shaft 202 in one direction or the other depending upon the direction of rotation of the motor to thereby cause pivotal movement of bell crank 212 about its pivotal connection 218 to support bracket 214.

Since the pivotal connection 216 of the bell crank 212 to the moving nut 210 moves along an arcuate path, it is necessary that this arcuate movement be accommodated and this is done by mounting the motor 54, planetary reducer 200, shaft 202 and associated bearings on support 215 which is pivotally movable about the pivotal connection 221 at the upper end of the support arm 214, as previously mentioned.

APPARATUS AND CONTROLS TO AUTOMAT- ICALLY MAINTAIN STEAM TEMPERATURE AT PRESET VALUE As shown in the control diagram of FIG. 1, a water admission valve generally indicated at 300 is provided to control the admission of cooling water to the cooling water manifold. The water admission valve 300 is controlled by control loops B and C which are indicated by a block diagram in FIG. 1, but which will be described in more detail hereinafter.

As best seen in FIG. 9, the cooling water admission valve includes a valve element 302 at the lower end of the valve stem 304, and movable within a valve chamber 305. Valve element 302 controls the passage of cooling water from the inlet passage 306 which. is connected to a suitable supply of cooling water such as the boiler feed pump discharge, to outlet passage 308 which leads to the desuperheater water manifold 62. The valve structure includes a bracket 310 mounted above the valve chamber. An air cylinder 311 is carried by the upper end of bracket 310. Lever members 312 are pivotally connected to the bracket 310 at point 314. The opposite end of levers 312 are pivotally connected by trunnions 316 to a nut member 318 which is linearly movable along the power screw member 320 driven by a motor 322 which in turn is swivelly mounted by trunnions 324 to a support bracket 326 which extends from the upper end of cylinder 311. The upper edge of lever 312 carries a limit switch LS-4 which is actuated by an adjustable stop member 328 carried by the lower end of air cylinder 311 and the lower edge of the lever 312 carries a limit switch LS5 which cooperates with an adjustable stop member 330 carried by the lower portion of the bracket 310. The stop members 328 and 330 respectively limit the upward and downward movement of lever 312, of valve stem 304 and of valve 302 connected to lever 312. A piston 334 is carried by the upper end of valve stem 304 and is movable in cylinder 311. A spring 336 in cylinder 311 biases piston 334 in a downward direction.

A trunnion ring 337 is coaxially positioned about valve stem 304 and is connected by pintles 339 to the spaced levers 312. Valve stem 304 is free to move vertically with respect to trunnion ring 337. A limit switch LS-ll iS carried by trunnion ring 337. A collar 338 is fixed to valve stem 304, whereby upward movement of valve stem 304 is limited by the engagement of collar 338 with the under surface of trunnion ring 337.

In normal operation, air is admitted through conduit 340 to air cylinder 311 beneath piston 334 to constantly urge valve stem 304 in an upward direction to a limiting position in which collar 338 abuts against trunnion ring 337, Valve 302 can never be opened faster or beyond a limited opening position as determined by the abutment of collar 338 with trunnion ring 337.

To control the admission of air through conduit 340 into the space beneath piston 334, there is provided an air valve mechanism or pneumatic operator generally indicated at 350 (FIG. 9), incluling a slidably movable valve element 352 which, in the position shown in FIG. 9, establishes communication between an air supply line 360 connected to the valve and the conduit 340 which is in pneumatic communication with the space beneath piston 334 in cylinder 311. Valve element 352 is maintained in a position in which it admits air beneath piston 334 when solenoid 8-12 is energized (see wiring diagram of FIG. 12).

When it is desired to close the cooling water admission valve 302 quickly to shut off further flow of cooling water, as in an emergency, for example, solenoid S12 is deenergized, as will be explained hereinafter in connection with the discussion of FIG. 12 of the drawings, permitting spring 362 to move the valve element 352 downwardly to a position in which the valve portion 353 establishes communication between conduit 340 and the air discharge ports 364, to thereby release the pneumatic pressure from beneath piston 334, to permit spring 336 to push piston 334 downwardly to thereby move valve element 302 to a fully closed position.

As seen in the view of FIG. 9, limit switch LS11 is supported by the trunnion ring 337 surrounding valve stem 304 so that it will operate when the pneumatic lifting out of the valve 302 causes the collar 338 on the valve stem to strike trunnion ring 337.

As seen on the wiring diagram for control loops B and C (FIG. 11), limit switch LS-ll has two normally open contacts (LS11a and LS11d) and two normally closed contacts (LS-11b and LS-11c).

Whenever collar 338 on valve stem 304 loses contact with trunnion ring 337, the normally closed contact LS- 11c closes in series with normally closed contact LS5 to energize solenoid S5 which operates the down circuit operating motor 322 to move operating levers 312 down to restore contact. At the same time LS-11c closes, LS- 11d opens to prevent energization of the circuit which moves operating levers 312 in an opening direction.

When contact is restored between collar 338 of valve stem 304 and the trunnion ring 337 on the operating levers 312 of the water admission valve apparatus mechanism, normally closed contact LS-llc will open and stop movement of motor 322, and a normally open contact LS-lld will reclose. This feature automatically prevents excessive opening of the water admission valve 302 when the valve is reopened after an emergency closing by the pneumatic operator because the control circuit to open the valve cannot function until the trunnion 337 on operating levers 312 are in contact with the collar 338 on the valve stem.

Whenever collar 338 on the valve stem loses contact with the trunnion ring 337 on operating levers 312, normally closed limit switch contact LS-11b (FIG. 11) will close to operate warning signal light L-7. When contact is restored between collar 338 and trunnion ring 337 normally open limit switch contact LS11a will close to operate signal light L6 which indicates that control is in normal operating condition with the collar on the valve stem in contact with the trunnion ring on the operating lever.

THE STEAM TEMPERATURE CONTROLLER The steam temperature controller which operates the motor 322 which controls the position of the operating levers 312 to control the opening of water admission valve 302 (FIG. 9) is shown schematically in FIG. 10 of the drawings. The steam temperature controller is generally indicated at 400 and includes a cam 401 which rotates in direct proportion to changes in the actual steam temperature as detected by the temperature transducer TT-5 shown on FIG. 1. Temperature transducer IT-5 is a thermocouple which generates a small voltage or current proportional to the temperature which it is detecting. This current is passed through an electronic amplifier which moves a slide wire by a motor until it produces a balanced voltage which matches the thermocouple voltage. The movement of the motor which moves the slide wire to balance the thermocouple voltage is also utilized to drive the cam 401.

The cam 401 has a pointer 402 which reads directly on a temperature scale to indicate the actual detected tem perature. It also operates four limit switches LS-7, LS-8, LS-9 and LS-10. The four limit switches are mounted on a ring gear 404 which rotates about the same center of rotation as cam 401. Ring gear 404 has a pointer 406 which is used to establish the preset control temperature on the same scale that the pointer 402 on cam 401 uses to indicate the actual temperature. When the actual temperature and the preset temperature are the same, all four limit switches on the ring gear are in normal free unactuated position. All four limit switches LS-7, LS-S, LS9 and LS-10 have one normally open contact and one normally closed contact.

When the actual temperature becomes 10 F. lower than the preset temperature, cam 401 will rotate sufiiciently to operate limit switch LS-S. As seen on the Wiring diagram of FIG. 11, limit switch contact LS-8a is in series with gang 3 of control switch CS-2 and also in series with normally closed limit switch LS5 carried by the cooling water admission valve mechanism (FIG. 9) so that closure of contact LS-8a will complete the circuit through limit switch LS-5 and gang 3 of control switch CS-2 to energize solenoid 8-5 which actuates contacts in the circuit of motor 322 of the cooling water admission valve to cause that motor to move the levers 312, and hence valve 302 in a valve closing direction to reduce flow of cooling water to the desuperheater water manifold. Contact LS8b Will open to turn off light L-10 which, when lighted, indicates that actual temperature is within plus or minus 10 F. of the control range. When the water admission valve 302 closes, the actual temperature of the steam should start to rise. When it returns to within 10 F. below the preset temperature, cam 401 will have rotated sufficiently to open limit switch LS-S and contact LS8a thereof to stop motor 322, and limit switch LS-Sa will close to relight signal light L-10 which indicates that the steam temperature is within the control range.

When the actual temperature of the steam becomes 10 F. higher than the preset temperature, cam 401 will rotate sufiiciently to operate limit switch LS-7 to cause the closing of the contact LS-7a. As seen on FIG. 11, when contact L'S7a of limit switch LS7 is closed, it completes a circuit through limit switch contacts LS-4 and LS-lld and through gang 2 contactor of control switch CS-2 in either its No. 3 or No. 4 position to complete the circuit through solenoid 8-6 to close the circuit of motor 322 in a direction which causes opening movement of valve 302. When the water admission valve 302 opens, the actual temperature of the steam should start to drop. When it returns to within 10 F. above the preset temperature, the cam 401 will have rotated sufficiently to open limit switch LS-7 and contact LS-7a will open to open the circuit of solenoid S6 to thereby stop the opening movement of valve operating motor 322. Also contact LS-7b will close to relight signal light L-10 which mdlcates that the control temperature is within the control range.

If the actual temperature ever reaches 50 F. below the preset temperature, cam 401 will rotate enough to operate limit switch LS10, closing contact LS-10a to operate signal light L11 which indicates that the actual temperature is too low (FIG. 11). Limit switch contact LS-10b will open to deenergize solenoid 8-7 which, in turn, deenergizes solenoid S12 to cause dumping of the air beneath the piston 334 of the cooling water admission valve 302 to thereby cause valve 302 to close by spring action (see FIGS. 9 and 12). Opening of contact LS-10b with consequent deenergization of solenoid S7 will also deenergize solenoid S-13 to cause the dumping of the air pressure in chamber 467 of the cooling water dump 13 valve 450 (FIGS. 1 and 13). The cooling water dump valve 450 will then open by spring action. This dual action of closing water admission valve 300 and opening water dump valve 450 stops all flow of cooling water to the desuperheater.

When the actual temperature returns to less than 50 F. below preset temperature, cam 401 rotates to move out of engagement with limit switch LS- permitting contact LS-10b to reclose. Solenoids S-12 and 8-13 will then be reenergized and air pressure will be restored to both the water admission valve 300 and to water dump valve 450 so that the water admission valve reopens and the water dump valve recloses.

If the actual temperature ever reaches 50 F. above the preset temperature, cam 401 will operate in a clockwise direction with respect to the view in FIG. 10 to operate limit switch LS-9 to close contact LS-9a which operates signal light L12 (FIG. 11) which is a warning light to indicate that the actual temperature is too high.

As previously described, steam temperature controller 400 (FIG. 10) has two pointers 402 and 406. Pointer 406 indicates the desired preset control temperature. The preset control temperature can be manually changed by rotating the knob 408 which rotates ring gear 404. The preset control temperature can also be automatically changed according to a time schedule by a reversible gear motor drive diagrammatically indicated in FIG. 10 as including a reversible motor 410 having an output gear 412. Gear 412 engages a gear 414 which is mounted on the same shaft as a gear 416 which, in turn, is in geared engagement with the ring gear 404 to either increase or decrease the present control temperature at a predetermined slow rate in accordance with the direction of rotation of motor 410.

Control switch CS-S (FIG. 11) is a three position, two gang switch which selects either Manual, Automatic Increasefor Automatic Decrease for the mode of establishing the preset temperature.

The preferred rate of change in preset temperature is between 50 F. per hour (the lowest) and 150 F. per hour (the highest). It would be desirable to be able to select any rate of temperature change between these limits for the automatic change of preset control. This can be done by using equipment which can provide an adjustable intermittent contact to the circuit of driving motor 410 for the ring gear 404. For this purpose, control switch CS-9 is provided (FIG. 11) and is shown as a five position, single gang switch which is used to select one of five different rates of temperature changes. These are, in the example shown, 50, 75, 100, 125 and 150 F. change per hour. The different rates of temperature change are obtained by connecting the circuit through different combinations of cam operated make and break limit switches to obtain different operating times for the motor 410 which rotates the ring gear 404. When control switch CS-5 is in Automatic Decrease position it energizes solenoid S8 in series with control switch CS-9 to control the circuit of motor 410 which moves gear 404 in a preset temperature decrease direction; and when the control switch CS-S is in the Automatic Increase position solenoid S9 is energized in series with control switch CS-9 to elfect the energization of the circuit of motor 410 to move gear 404 in preset temperature increase direction. When control switch CS-S is in either the Automatic Increase or the Automatic Decrease position gang 2 of switch CS-S energizes solenoid S-11 which controls the circuit of the motor which rotates the cams which operate the limit switches associated with switch CS-9 to provide the intermittent operation of motor 410 which rotates ring gear 404.

CONTROL CIRCUITS TO AUTOMATICALLY MAINTAIN STEAM TEMPERATURE AT PRESET VALUE Control loops B and C of FIGS. 1 and 11 These controls include the operating and monitoring devices for setting and controlling the main line steam temperature to the turbine. The schematic wiring diagram of these devices is shown on FIG. 11.

Control switch 08-3 is On-Off master switch which connects control power to all of the control devices in control loops B and C.

Control switch CS-6 is a key lock On-Off switch which is in series with CS3- to prevent accidental unwanted closing of CS-3.

When CS3 is in Oil position, signal light L-8 indicates that controls and operators are deactivated.

When CS3 and CS6 are closed, signal light L-9 indicates that the controls and operators are connected to control power.

Control switch CS2 is a 3-gang, 4-position switch and is used to operate signal lights and switch on the automatic opening and closing control circuits for the cooling water admission valve 302.

When CS-2 is in Off position contact 1 in gang 1 energizes signal light L4 to indicate that this control is deenergized. The same contact 1 of gang 1 also completes the circuit through conductor 500 and limit switch LS5 associated with the cooling water admission valve 300 (FIG. 9) to solenoid S5 (FIG. 11) which energizes the circuit of motor 322 (FIG. 9) which moves control levers 312 associated with water admission valve 300 in a closing direction until the motor 322 is deenergized by the engagement of normally closed limit switch LS-5 with stop member 330.

When CS2 is in Off position (position 1) gang 2 and gang 3 are not connected to any circuitry, other than lights L4 and L-S.

When (35-2 is in Close Only position (position 2), signal light L-5 is energized through gang 1 to indicate that the control is energized. Gang 2 is not connected. Gang 3 closes the circuit through terminal 2 of gang 3 and conductor 500 to energize solenoid S5 through limit switch contact L's-8a of steam temperature controller 400 (FIG. 10) hereinbefore described. This circuit also includes limit switch LS-S. Energization of solenoid S5 closes the circuit of motor 322 (FIG. 9) to cause movement of lavers 312 in a valve closing direction. As was pointed out in connection with the description of the steam temperature controller (FIG. 10), limit switch LS-8 is actuated when the temperature becomes 10 lower than the preset temperature.

When CS-Z is in Close and Slow Open position (position 3), the contacts of gang 1 energize light L-5. In position 3 of CS-2, gang 2 closes the circuit to solenoid S6 to permit limit switch LS-7a of the steam temperature controller (FIG. 10) to automatically Slow open the motor operated cooling water admission valve 302. LS-7a is operated to closed position by the steam temperature controller of FIG. 10 when the actual temperature exceeds the preset temperature by 10 F., as described in connection with FIG. 10. Gang 3 completes the circuit to solenoid S6 as just described in series with an interrupter device 502, comprising a motor 8-10 which drives a cam to periodically interrupt limit switch LS-16 in series with solenoid S6 so that the circuit of motor 322 whch causes movement of water admission valve 302 in the opening direction through movement of operating levers 312 is energized only intermittently. This intermittent operation provides Slow Opening action of valve 302.

When CS-2 is in Close and Fast Open position (position 4), gang 1 energizes light L-5 and gang 2 provides a direct connection to solenoid S6 which controls the water inlet valve opening circuit of motor 322 if energization of this circuit is called for by the closure of limit switch LS-7a by temperature controller 400 of FIG. 10 (limit switch LS-7a is closed when the actual temperature is 10 F. higher than the preset temperature). In the Close and Fast Open position (position 4) of switch CS-2, gang 3 closes the circuit of solenoid S5 in series with steam temperature controller contact LS-8a and limit switch LSS. Closure of solenoid S energizes the circuit of motor 322 (FIG. 9) to cause movement of levers 312 in a valve closing direction, assuming that contact LS8a is closed. As pointed out in connection with the description of FIG. 10, limit switch contact LS8a is closed when the actual temperature is F. lower than the preset temperature.

Control loops D, E, F, and G shown on FIGURES 1 and 12 Schematic wiring diagrams for control loops D, E, F and G are shown on FIG. 12.

These protective controls are provided to prevent excessive cooling of the steam in cases of turbine tripout, a boiler tripout, a sudden decrease in turbine load with a reduction in main line steam flow, or a malfunction in the steam temperature control that could result in an excessive admission of cooling water.

The required protection is obtained by dumping the air in chamber 467 of the cooling water dump valve 450 to quickly open this valve by spring action. A protective backup is also obtained by dumping the air in chamber 333 of the cooling water admission valve 300 to obtain rapid closing of this valve by spring action.

The cooling water admission valve is shown in FIG. 9 and was previously described.

There is shown in FIGS. 1 and 13 the cooling water dump valve generally indicated at 450 which bypasses cooling water from conduit 308 leading to the cooling water manifold 62 of the desuperheater through conduits 454 and 456 to the condenser 458. The water dump valve 450 comprises a valve chamber 452 which is connected by conduit 454 to conduit 308. The outlet of the valve chamber 452 is connected by conduit 456 to condenser 458. A valve element 460 is movable in the valve chamber 452 to cut off communication between conduits 454 and 456 when the valve element 460 is in closed position. Valve element 460 is carried by a valve stem 462 which projects upwardly into a control casing 464. A diaphragm 466 is carried on the upper end of valve stem 462. A spring 469 engages an abutment or collar 471 on valve stem 462 and biases valve 460 to an open position. Pneumatic pressure is admitted to the space 467 above the diaphragm 466 through a conduit 468 which communicates with a pneumatic operator generally indicated at 470. The pneumatic operator 470 includes a movable valve member 472 which is normally maintained in a raised position against the force of spring 478 when solenoid 8-13 is energized (see control diagram of FIG. 12). When solenoid 5-13 is energized and valve member 472 is in the raised position as just mentioned, pneumatic communication is established between the inlet port 476 and the outlet port 474 of the pneumatic operator 470 to thereby supply pneumatic pressure through conduit 468 to the space 467 above the diaphragm 466 to 'move valve element 460 of the water dump valve to a closed position. When solenoid S13 becomes deenergized, spring member 478 moves valve member 472 downwardly to place the discharge ports 480 of the pneumatic operator 470 in communication with conduit 468 and with the space 467 above diaphragm 466, to thereby dump the air from chamber 467, permitting spring 469 to move valve element 460 to an open position in which the water is dumped or discharged from conduit 308 to conduits 454 and 456 through the valve chamber 452 and hence to the condenser 458.

As seen on the wiring diagram of FIG. 12 of the drawings, solenoid S7 controls the energization condition of solenoids S12 and S13 which respectively control the dumping of air for the water admission valve 302 (FIG. 9) and the dumping of air from the chamber 467 of the water dump valve 460 to respectively permit closing of the water admission valve 302 and opening of the energized condition in series with normally closed limit switches LS15, LS16, LS17 and LS10b. When energized, solenoid S7 closes the normally open contacts S7a and S7b. Contact S-7a is in series with solenoid S12 associated with the pneumatic operator 350 for water admission valve 302, while contact S7b is associated and in series with solenoid S13 for the pneumatic operator 470 of water dump valve 460. When solenoid S12 is deenergized by the opening of contact S7a, valve element 352 of pneumatic operator 350 is moved by spring 362 to the position in which it dumps the air from the chamber 333 (FIG. 9) to permit spring 336 to close water admission valve 302.

When solenoid 5-13 becomes deenergized by the opening of either limit switch LS14 or of contact S7b, valve 472 is moved by spring 478 (FIG. 13) to a position in which the air in chamber 467 of water dump valve 460 is dumped to permit spring 469 to open water dump valve element 460. Limit switch LS14, connected in series with solenoid 8-13, is operated by a trip lever CS7 located on the desuperheater control panel. When trip lever CS7 is pushed in one direction, it opens limit switch LS14 to open the circuit of solenoid 8-13 and thereby quickly open water dump valve 460. When trip lever CS7 is moved in the opposite direction, it closes limit switch LS14 to reenergize solenoid S13, assuming that contact S7b is closed.

As previously mentioned, solenoid S7 which controls the energization and deenergization of solenoids S12 and S13 is connected across the power supply in series with four limit switches, namely LS15, LS16, LS17 and LS10b. Each of these four limit switches is normally closed. If any one of the four limit switches just mentioned is opened, solenoid S7 becomes deenergized, causing water admission valve 302 to close and causing water dump valve 460 to open.

Switches LS-15 and LS16 are opened by a turbine trip signal and a boiler trip signal, respectively. Limit switch contact LS10b is opened when the steam temperature controller 400 (FIG. 10) actuates limit switch LS10 in response to the detection by sensing device TT-S of a downstream steam temperature which is 50 below the preset temperature. This action is reversible.

Limit switch LS17 is opened by a special control on the turbine governor valve operator which activates LS17 to open position when the turbine load is dropped, and the turbine governor valves close quickly. When the turbine valves close slowly, limit switch LS17 will not be activated.

There is shown on FIG. 14 of the drawings a control operator which may be used to operate switch LS17 in response to a fast closing action of the turbine governor valves, as a protection against excessive steam cooling due to sudden load drip on the turbine. The turbine turbine-governor valve operating rod is indicated at 600 in FIG. 14. Rod 600 moves upward to close the governing valves of the turbine. A collor 602 is mounted on rod 600. Mounted adjacent the path of movement of rod 600 is a control device generally indicated at 604 comprising a bell crank generally indicated at 606 and pivotally mounted at point 608 on a stationary support arm 610. The bell crank 606 includes arms 612 and 614, respectively. At the outer end of arm 612 of the bell crank there is pivotally mounted at point 618 a short extension lever 616. Lever extension 616 has rigidly attached thereto a fork or angle member generally indicated at 620 including an arm 622 and an arm 624. The outer end of lever extension 616 carries a roller member 626. A spring 628 is received in a recess or cavity in the outer end of arm 612, the lower end of spring 628 bearing against the surface of arm 624 of the fork 620 on lever extension 616 so that the spnrig 628 biases lever extension 616 in a clockwise direction about its pivot point 618, with respect to the view shown in FIG. 14, causing roller 626 to bear against collar 602. An adjust- 17 able stop 629 limits the pivotal movement of lever extension 616 and fork 620 in a counterclockwise direction with respect to the view of FIG. 14. A limit switch LS-17 is mounted on the upper edge of the arm 612 of hell crank 604.

A dashpot generally indicated at 630 is supported by the lower end of bracket member 610 and piston member 632 is movable in the dashpot by means of a piston rod 634 which is pivotally connected at its outer end at 636 to the lower or outer end of arm 614 of bell crank 606.

At the outer end of the dashpot 630 is mounted a spring loaded, one-way air valve generally indicated at 640 which controls the flow of air through air passages 642 in the end wall of the dashpot. The valve comprises a closure or valve element 644 mounted on a valve stem 646, valve stem 646 including a base portion or spring seat 648. Spring 650 is interposed between the facing surfaces of spring seat 648 and of the end wall of the dashpot, whereby to bias the valve element 644 in the closed position shown in FIG. 14, in which position air air flow through the passages 642 into the interior of the dashpot is prevented.

In the operation of the device of FIG. 14, when the rod 600 moves downwardly to open the governing valves of the turbine, the collar 602 of rod 600 abuts against the roller 626 and causes the lever extension 616 and the lever arm 612 of the bell crank 606 to move downwardly together about the pivot point 618 to thereby cause a movement of the piston and piston rod 632 and 634 against the force of the spring 635 of the dashpot. Movement of the piston 632 as described causes one-way valve 640 to open to admit air into the dashpot chamber 631 through passages 642.

When rod 600 moves upwardly to close the governing valves, the spring biased lever extension 616 and the roller 626 thereon will follow the movement of the rod 600 as long as movement of rod 600' does not occur too quickly. If rod 600 moves up to close the governor valves too quickly, as would be caused by a sudden load drop on the turbine, the roller or rollers 626 on the lever arm 616 will lose contact with collar 602 on rod 600 because piston 632 cannot displace the air in the dashpot fast enough. The lever extension 616 of the bell crank will then rotate about the pivot point 618 to operate the limit switch LS-17 (FIG. 12) to open position to deenergize solenoid S-7, causing water admission valve 302 to close and causing water dump valve 460 to open.

Excess water removal controls As a backup protection against a possible desuperheater malfunction which could result inunevaporated water being present in the steam header downstream of the desuperheater, excess water removal equipment is provided as shown diagrammatically on FIG. 1 of the drawings and controlled by control circuitry shown on FIG. 12 of the drawings. The surplus water removal equipment includes a surplus water removal conduit 17 which is connected to the downstream portion of steam line 16 by a T connection indicated at 19. A surplus water drain valve 21 is connected in conduit 17. The valve 21 is operated by a reversible motor controlled by solenoids S-3 and S4 of FIG. 12. Thus solenoid S3, when energized, energizes the valve open circuit of the drain motor, while solenoid 8-4, when energized, energizes the valve close circuit of the drain valve motor. Control switch CS8 is provided to selectively energize either solenoid S-3 or 8-4 to move the valve operating motor for valve 21 in either the opening or closing direction. Switch CS-8 is also movable to an intermediate position in which the valve is held in any position between fully opened and fully closed positions. The use of the motor operator for the drain valve permits an easy setting of the valve for any opening between Wide open and fully closed. This is desirable because when the desuperheater is in service, the drain valve should not be opened more than necessary to insure good water removal so as to avoid excessive bypassing of header steam.

Limit switches LS-12 and LS-13 are mounted on the motor operated drain valve (FIG. 12) and operate signal lights L 13 and L-14 to indicate that the valve is in closed and open position, respectively.

As seen in FIG. 12, a Power-stat generally indicated at 550 comprising a variable inductance 552 is connected across an alternating current power source, and includes a pointer 554 which is rotated in accordance with the closing and opening movement of the motor operated drain valve 21. A voltmeter 556 is connected across one side of the alternating current power source and across the voltage between one end of the inductance and the pointer as an indication of the actual positions between fully opened and fully closed of the surplus water drain valve 21.

PRESSURE AND TEMPERATURE DETECTION AND INDICATING DEVICES OF DESUPER- HEATER SYSTEM The following is a summary of the pressure and temperature sensing and indicating devices of the desuperheater system as seen on FIG. 1 of the drawings.

Pressure sensing device PT-l is connected to conduit 12 between the boiler and the desuperheater upstream of the desuperheater, and communicates pressure conditions at this point to control loop A and more specifically to the control device 110 shown in FIG. 6 of the drawings. Pressure sensed at PT-l is also communicated to a pressure indicating device PI-1 on the control panel.

A temperature sensing device TT-l is also connected to conduit 12 between the boiler and the desuperheater upstream of the desuperheater, temperature sensing device TT-l being connected to an indicator TI1 on the control panel of the desuperheater system.

Pressure sensing device PT-2 measures the steam pressure a short distance downstream of the. desuperheater and is connected to control loop A and more specifically to the control device 110 shown in FIG. 6 of the drawings. Pressure sensing device PT-2 is also connected to a pressure indicating device PI-2 on the control panel of the desuperheater system.

The pressure sensing device PT-3 senses the steam pressure in the steam line 22 adjacent the turbine throttle and is connected to an indicating device PI3 on the control panel. This pressure is needed to determine the saturation temperature of the steam at that point. The minimum temperature at which the pointer 406 of steam temperature control device (FIG. 10) can be set for automatic control would be saturation temperature plus 50 F. Throttle pressure (PI3) and the steam pressure immediately after the desuperheater (PI-2) should read approximately the same except for some small line pressure dro T he temperature sensing device "FF-2 senses the steam temperature at the turbine throttle, and is connected to indicator TI2 on the desuperheater control panel. The difference between the indicated temperatures TI-l upstream of the desuperheater and TI2 at the turbine throttle is an indication of the cooling accomplished by the desuperheater.

Temperature sensing device TT3 measures the turblne inlet metal temperature and is connected to temperature indicator TI3 on the desuperheater control panel.

The temperature sensing device TT4 measures the turbine inlet steam temperature and is connected to indicating device TI4 on the desuperheater control panel. The steam temperature to the turbine is being properly controlled when indications TI3 and TI4 are not more than apart. During transient conditions when starting, these temperatures may occasionaly show more than 100 difierential while control is becoming stabilized. Temperature sensing device TT-S senses the steam temperature at the throttle valve of the turbine and is connected to control loops B and C and more particularly to the input circuit of the steam temperature controller 400 (FIG. to control the rotary motion of steam temperature control cam 401. Pressure indicator PT3 measures the pressure in steam line 22 leading to the turbine throttle and thus indicates steam turbine pressure at the turbine throttle.

Pressure sensing device PT4 measures the cooling water pressure available at the inlet to the cooling water admission valve 300. This pressure should always be higher than the header steam pressure upstream of the desuperheater as measured at point PT-l and as indicated on indicator PI-l.

SUMMARY OF OPERATION The following is a summary of the principal features of the operation:

With steam passing from boiler 10 through conduit 12 and through the desuperheater casing 14 and conduits 16 and 22 to turbine 18, control loop A (FIG. 1) is activated by moving control switch CS1 (FIG. 7) to On position to make possible the operation of the solenoids S-1 and S2 (FIG. 7) which control the reversing motor 54, which in turn actuates operating mechanism 52 to control the position of desuperheater valve plug 38. The steam pressure at points PT1 and PT2 respectively upstream and downstream of the desuperheater are communicated to the pressure responsive device 110 (FIG. 6). If the pressure differential between PT1 and PT2 is greater than a predetermined value such as 125 p.s.i., diaphragm 116 of the pressure sensitive device 110 will be moved to close limit switch LS-l to cause energization of solenoid Sl to cause reversing motor 54 and valve plug operating mechanism 52 to move the valve plug 38 in a upward direction to increase the size of the restricted steam passage area X adjacent the valve plug to thereby cause the pressure differential between PTl and PT2 to be restored to the proper range. On the other hand, if the pressure differential between PTl and PT2 drops to a predetermined value such as 75 p.s.i., for example, diaphragm 116 of the pressure control device 110 will move in a direction to operate limit switch LS-2. Operation of limit switch LS-2 will energize solenoid S2 to cause operation of reversing motor 54 and valve operating mechanism 52 in a direction which lowers the valve plug 38 to thereby reduce the restricted steam passage area adjacent valve plug 38 to thereby restore the pressure differential between PT1 and PT2 to a proper value, such as 100 p.s.i.

By maintaining the steam pressure differential across the desuperheater plug 38 at a predetermined optimum value, such as 100 p.s.i. plus or minus 25 p.s.i., atomization and evaporation of the cooling water injected into the restricted throat region contiguous the valve plug 38 will be obtained. The control loop A will maintain the proper pressure drop across the restricted passage automatically and when the steam flow through the header changes, due to load change on the turbine or due to changes in steam pressure, the control loop will automatically readjust the plug position to maintain the required pressure drop for the neW steam flow. Once the operator places the control loop A in service, it will require no further attention other than to occasionally check to see that it is automatically maintaining the desired pressure drop across the restricted passage. This will be indicated b pressure gauges (PI-1 and PI-2) and by signal light L-3 on the control panel.

Cooling water is admitted to the desuperheater cooling water manifold 62 from a source such as the boiler feed pump discharge, the cooling water passing through conduit 306 and through the water admission valve generally indicated at 300, thence through conduit 308 and nonreturn valve 309 (FIG. 1) to the ooling water manifold 62 of the desuperheater. Nonreturn valve 309 prevents an outflow of header steam when the dump valve 460 opens.

The water admission valve 300 is controlled by control loops B and C (FIG. 11). These control loops are energized by closure of control switch CS3 and by closing series connected key locked switch CS6 to place in operation the control circuitry which controls the opening and closing of cooling water admission valve 300.

The operator positions the pointer 406 at the desired preset steam temperature on the temperature scale of temperature control device 400 (FIG. 10). To determine the setting of pointer 406, the operator reads the metal temperature inside the turbine as sensed by sensing device TT3 (FIG. 1), and as indicated on indicating device TI-3 and sets pointer 406 of the steam temperature control device 400 at a setting which calls for a steam temperature having a predetermined differential such as F., for example, above the metal temperature as indicated by indicator TI3. Cam 401 of the steam temperature control device 400 rotates in accordance with the actual temperature measurement of the steam temperature sensed by sensing device TT-S (FIG. 1). If the actual temperature becomes 10 F. lower than the preset temperature, cam 401 will rotate sufficiently to operate limit switch LS-8, to energize solenoid S5 through control switch CS2 in any one of the positions 2, 3, 4, thereof (FIG. 11) which actuates contacts in the circuit of motor 322 (FIG. 9), to cause movement of the cooling water admission valve 302 in a valve closing direction, to thereby reduce the flow of cooling water into the desuperheater cooling water manifold 62.

If the actual temperature of the steam as measured by sensing device TT-S becomes 10 F. higher than the preset temperature, cam 401 will rotate sufficiently to operate limit switch LS7 to cause the energization of solenoid S6 which energizes the circuit of motor 322 to cause opening movement of the water admission valve 302 to increase the cooling water supplied to the steam, so that the temperature of the steam should start to drop. The circuits to the solenoids S6 and S5 (FIG. 11) are controlled through a control switch CS2 which when placed in position 3 of the switch provides for slow opening of the water admission valve 302 by connecting the solenoid S6 which controls the valve opening circuit of motor 322 in series with an interrupter device 502 which periodically interrupts the energization circuit of solenoid S6 to provide a slow opening of the water admission valve 302. When placed in position 4, control switch CS2 provides for fast opening of water admission valve 302 by bypassing interrupter device 502.

If the actual temperature ever reaches 50 F. below the preset temperature, cam 401 of the steam temperature control device 400 will open limit switch contact LS-10b to deenergize solenoid 8-7, in turn deenergizing solenoids S12 and S13, to cause closing of the cooling water admission valve 302 and opening of the cooling water dump valve 460 (FIGS. 1 and 13).

The steam temperature control device 400 may also be automatically operated to provide a controlled rate of steam temperature increase, when the turbine is being loaded, or a controlled rate of steam temperature decrease, when the turbine is being unloaded. This is accomplished by moving control switch CSS (FIG. 11) to either Automatic Increase position or Automatic Decrease position. In the Automatic Increase position, solenoid S9 is energized to energize the circuit of motor 410 which moves the ring gear 404 of the steam temperature control device 400 in a preset temperature increase direction. When control switch CS-S is moved to the Automatic Decrease position, solenoid S-8 is energized to energize the circuit of motor 410 to move ring gear 404 in a preset temperature decrease direction. In either the Automatic Increase or Automatic Decrease positions, the respective solenoids S8 and S9 are connected in series with switch CS9 in one of its positions to thereby electrically connect one of a plurality of cam operated make and break limit switches in series with the solenoid S-8 or 8-9, whereby to obtain different operating times for the motor 410 which rotates the ring gear 404 of the temperature control device 400. This permits the selection of different rates of temperature change, as, for example, 50, 75, 100, 125 and 150 F. change per hour.

When control switch CS-S is in either the Automatic Increase or Automatic Decrease position, solenoid S11 is energized in series with switch CS-S (FIG. 11) to cause the energization of the motor which rotates the operating cams for the make and break limit switches of switch CS-9 which provide different operating times for the motor 410 which rotates the ring gear 404, and thus provide different rates of temperature increase or decrease.

In the embodiment of FIG. 3, the cooling water manifold 62 of the desuperheater discharges cooling water through nozzles 70 into the main steam flow in the region of the adjustable high velocity restricted passage X, the

flow of cooling water being adjusted by the water admission valve 300 under the control of control loops B and C.

In the modified embodiment of FIG. 4, the cooling water is mixed with bypass steam passing through inlet openings or passages 100 which communicate with the main steam flow upstream of the adjustable valve plug 38. This bypass steam mixes with the cooling water and atomizes it in the mixing chamber 74' before the mixture is injected into the main line of steam flow, Where the water-steam mixture is there subjected to a second steam atomizing action to get optimum evaporation of the water. This premixing of the cooling water with the bypass steam causes the temperature changes in the desuperheater casing to be less drastic, and reduces the possibility of thermal shock in the casings containing the main steam flow.

Protective controls are provided to prevent excessive cooling of the steam in cases of a turbine tripout, a boiler tripout, a sudden decrease in turbine load with a reduction in main line steam flow or a malfunction in the steam temperature control that could result in an excessive admission of cooling water. As seen on the wiring diagram of FIG. 12 of the drawings, solenoid 8-7 is in series with limit switches LS15, LS16, LS-17 and LS-10b which are respectively opened by a turbine trip signal, a boiler trip signal, a fast closing of the turbine governor valves which might be caused by sudden load drop on the turbine, and a detection by the sensing device TT- (FIG. 1) of a downstream steam temperature which is 50 F. below the preset temperature, indicating a malfunction in the steam temperature control. If any of these limit switches just mentioned opens, solenoid 3-7 is deenergized to thereby cause a deenerization of solenoids 8-12 and S-13 (FIG. 12) which respectively cause the closing of the water admission valve 302 (FIG. 9) and the opening of the water dump valve 460 (FIG. 13).

A surplus water drain valve 21 is connected in the conduit 17 which communicates with the steam line 16. Valve 21 is operated by a reversible motor controlled by solenoids S-3, S-4 (FIG. 12) under the control of control switch CS-S.

While there have'been shown and described particular embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein Without departing from' the invention and, therefore, it is aimed to cover all such changes and modifications as fall within the true spirit and scope of the invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In combination, a system including steam generating means, a steam turbine, conduit means connecting said steam generating means to said steam turbine, first temperature measuring means for measuring the temperature of steam entering said turbine, second temperature measuring means for measuring the metal temperature of said turbine, means for introducing cooling water into"the steam flow in said conduit means to obtain a predetermined temperature differential between the steam entering said turbine and the metal of said turbine, and means for varying the steam passage area of said conduit means in the region where said cooling water is introduced as a function of steam flow conditions in said conduit means, whereby to maintain substantially constant steam velocity in said region for optimum atomization of said cooling water.

2. The combination defined in claim 1 including means for progressively varying the temperature of the steam entering the turbine.

3. The combination defined in claim 1 in which said means for varying the steam passage area of said conduit means comprises a valvelike plug member mounted for axial movement in said region of said conduit means.

4. The combination defined in claim 1 in which said means for varying the steam passage area of said conduit means comprises a valvelike means, means for measuring the steam pressure at a point upstream of said valvelike means and at a point downstream thereof, and means for moving said valvelike means in response to the steam pressure differential between said points to vary the steam passage area of said region as a function of said differential.

5. The combination defined in claim 1 in which said means for introducing cooling water into the steam flow in said conduit means includes an annular cooling water manifold extending around the inner periphery of said conduit means, means connecting said manifold to a source of cooling water, said manifold having a plurality of outlet passages therein for passage of cooling water from said manifold into the steam flow in said conduitmeans.

6. The combination defined in claim 1 including means for bypassing steam into contact with said cooling water in advance of the passage of said COOllIlg water into the main steam flow, whereby to at least partially atomize said cooling water prior to passage thereof into the main steam flow.

7. A desuperheater apparatus for controlling the temperature of steam supplied to a steam utilization device such as a steam turbine or the like, comprising a steam conduit means, means for injecting cooling water into a regi n of said steam conduit means including a cooling water manifold extending around the inner periphery of said conduit means in said region, means connecting aid manifold to a source of cooling water, said manifold having a plurality of outlet passages therein for passage of cooling water from said manifold into the steam fiow in said steam conduit means, valve means for varying the steam passage area of said steam conduit means in the region where said cooling water is injected, and means for varying the position of said valve means as a function of the differential in a steam condition between a point of said steam conduit means upstream of said valve means and a point of said steam conduit means downstream of said valve means, whereby to maintain substantially constant steam velocity in said region for optimum atomization of said cooling water.

8. The combination defined in claim 7 in which said means for varying the steam passage area of said conduit means comprises a valvelike plug member mounted for axial movement in said region of said conduit means.

9. The combination defined in claim 7 in which said means for varying the steam passage area of said conduit means comprises a valvelike plug member mounted f r axial movement in said region of said conduit means, and means mounting said valvelike plug member for retraction out of obstructing relation to the steam flow path when said desuperheater apparatus is not in service.

10. The combination defined in claim 7 in which said means for varying the steam passage area of said conduit means comprises a valvelike means, means for measuring the steam pressure at a point upstream of said valvelike means and at a point downstream thereof,

and means for moving said valvelike means in response to the steam pressure differential between said points to vary the steam passage area of said region as a function of said differential, whereby to obtain substantially constant steam velocity in said region for optimum atomization of said cooling Water.

.11. The combination defined in claim 7 including means for bypassing steam into contact with said coolin water in advance of the passage of said cooling water into the main steam flow, whereby to at least partially atomize said cooling water prior to passage thereof into the main steam flow.

12. The combination defined in claim 7 including a plate member positioned in contact with the upper surface of said cooling water manifold around the periphery of said manifold, bypass steam passages in communication with the main steam flow extending through said plate member, a mixing chamber defined by spaced facing surface portions of said plate member and of said manifold, said mixing chamber communicating with said region of said conduit means, and separate passage means communicating said bypass steam passages and the interior of said cooling water manifold with said mixing chamber, whereby the bypass steam mixes with cooling water in said mixing chamber in advance of the passage of the cooling water into said region of said conduit means.

13. The combination defined in claim 7 in which said conduit means is provided with an annular recess for receiving said cooling water manifold and said cooling water manifold is secured in said recess with a minimum of surface contact between said manifold and said conduit means to minimize thermal shock to said conduit means.

14. The combination defined in claim 7 including cooling water conduit means for supplying cooling water to said cooling water manifold, said cooling water conduit means extending through passage means in said steam conduit means into communication with said cooling water manifold, and means radially spacing said cooling water conduit means from said passage means in said steam conduit means, whereby to minimize thermal shock to said steam conduit means.

15. A desuperheater apparatus for controlling the temperature of steam supplied to a steam utilization device such as a steam turbine or the like, comprising a desuperheater casing adapted to be connected in series with and forming part of a steam conduit between a steam generator and the steam utilization device, means for injecting cooling water into a region of said desuperheater casing including a cooling water manifold extending around the inner periphery of said desuperheater casing in said region, means connecting said manifold to a source of cooling water, said manifold having a plurality of outlet passages therein for passage of cooling water from saidmanifold into the steam flow in said desuperheater casing, a valvelike plu member mounted in said desuperheater casing for axial movement in said region of said desuperheater casing where said cooling water is injected, and means for axially moving said valvelike plug member in said region as a function of the diiferential in a steam condition between a p int of said steam conduit upstream of said valve means and a point of said steam conduit downstream of said valve means, whereby to maintain substantially constant steam velocity in said region for optimum atomization of said cooling water. 16. The combination defined in claim 15 in which said valvelike plug member is mounted for retraction out of obstructing relation to the steam flow path through said desuperheater casing when said desuperheater apparatus is not in service.

17. In combination, a system including a steam generating means, a steam turbine, steam conduit means connecting said steam generating means to said steam turbine, a desuperheater including a desuperheater casing connected in series with and forming part of said steam conduit means, means for injecting cooling water into a region of said desuperheater casing including a cooling Water manifold extending around the inner periphery of said desuperheater casing in said region, said manifold having a plurality of outlet passages therein for passage of cooling water from said manifold into the steam flow in said desuperheater casing, water conduit means connecting said manifold to a source of cooling Water including a water admission valve connected in series therewith, a valvelike plug member mounted in said desuperheater casing for axial movement in said region of said desuperheater casing where said cooling water is injected, and means for axially moving said valvelike plug member in said region as a function of the differential in a steam condition between a point of said steam conduit means upstream of said valvelike plug member and a point of said steam conduit means downstream of said valvelike plug member, whereby to maintain substantially constant steam velocity in said region for optimum atomization of said cooling water.

18. The combination defined in claim 17 including a water dump valve connected to said water conduit in bypass relation to said cooling water manifold whereby to prevent water flow to said cooling water manifold when said water dump valve is open, said water dump valve being closed during the normal operation of said desuperheater.

19. The combination defined in claim 18 including control means responsive to predetermined conditions in said system to simultaneously close said water admission valve and open said water dump valve.

20. A desuperheater apparatus as defined in claim 7 including means for presetting a desired temperature of steam entering the steam utilization device, means for sensing the actual temperature of the steam entering the steam utilization device, and means for controlling admission of cooling water into said region of said conduit means as a function of said actual temperature and of said desired temperature.

'21. A desuperheater apparatus as defined in claim 20 including means for variably presetting said desired temperature as a function of time.

22. In combination, a system including a steam generating means, a steam utilization device, steam conduit means connecting said steam generating means to said steam utilization device, a desuperheater including a desuperheater casing connected in series with and forming part of said steam conduit means, means for injecting cooling water into a region of said desuperheater casing including a cooling water manifold extending around the inner periphery of said desuperheater casing in said region, said manifold having a plurality of outlet passages therein for passage of cooling water from said manifold into the steam flow in said desuperheater casing, water conduit means connected to said cooling water manifold, means for presetting a desired temperature of steam entering the steam utilization device, means for sensing the actual temperature of the steam entering the steam utilization device, means for controlling admission of cooling water into said region of said desuperheater casing as a function of said actual temperature and of said desired temperature, a valve means mounted in said desuperheater casing for movement in said region of said desuperheater casing where said cooling water is admitted, and means for moving said valve means in said region as a function of the differential in a steam condition between a point of said steam conduit means upstream of said valve means and a point of said steam conduit means downstream of said valve means, whereby to maintain substantially constant steam velocity in said region for optimum atomization of said cooling water.

23. The combination defined in claim 22 including means for variably presetting said desired temperature as a function of time.

24. The method of controlling the temperature of steam supplied to a turbine during the starting and loading cycle which comprises the steps of measuring the metal temperature of the turbine, measuring the temperature of the steam supply to the turbine, injecting cooling water into the steam flow to reduce the temperature of the steam flowing to the turbine to a predetermined value in excess of the metal temperature which will not cause thermal stress to the turbine metal, and progressively increasing the temperature of the steam flow to the turbine by controlling the injection of cooling water into the steam flow until a predetermined maximum temperature of steam flow to the turbine is reached.

25. The method of controlling the temperature of steam supplied to a turbine during the unloading cycle which comprises the steps of measuring the metal temperature of the turbine, measuring the temperature of the steam supply to the turbine, injecting cooling water into 20 the steam flow to reduce the temperature of the steam flowing to the turbine to a predetermined value less than the metal temperature which will not cause thermal stress to the turbine metal, and progressively reducing the temperature of the steam flow to the turbine by controlling the injection of cooling water into the steam flow until a predetermined minimum temperature of steam flow to the turbine is reached.

References Cited UNITED STATES PATENTS 1,832,652 11/1931 Peebles.

2,355,458 8/ 1944 Mastenbrook.

2,725,221 11/ 1955 Pontow 26162 2,945,685 7/1960 BoWlus 26139 XR 3,220,708 11/1965 Matsui 122-479 XR 3,331,590 8/1967 Battenfeld et a1. 122-487 XR KENNETH W. SPRAGUE, Primary Examiner U..S. C1. X.R. 

